JP2005508101A - Electron beam excitation superconducting analog-digital converter - Google Patents

Abstract

Systems and methods are provided for fast conversion of an analog voltage signal into a digital representation with an A / D converter. The present invention teaches N superconducting, preferably HTC, N-bit A / D converters manufactured on transmission lines. N lines are arranged in parallel and adjacent to each other. In each line, 2 ^N-1 Josephson junction elements are embedded in series. The Josephson junction element forms a matrix on the configuration of the N superconducting transmission lines, generates the Josephson junction element along the X direction with an N-digit binary number, and further generates the N-digit binary number. The numbers are placed along the Y direction so that they are arranged in integer order. A scanning electron beam is generated to be applied to this array. This beam is scanned at a high frequency across the line and is deflected along the line by an applied voltage signal. The electron beam produces a voltage step on any one of the N superconducting transmission lines in a state where it hits one of the Josephson junction elements. By cross-scanning the beam in this way, a voltage pattern of N bit steps is generated on the line. The pattern is a direct digital reading of the input voltage signal.
[Selection] Figure 1

Description

【Technical field】
[0001]
The present invention relates to analog-to-digital conversion, and more particularly to systems and methods for high-speed analog-to-digital conversion.
[Background]
[0002]
Advances in digital processing have had a significant impact on many efforts in scientific and technical and digital processing applications. In many cases, it is necessary to convert a high-speed analog signal into a digital representation in order to utilize and process the capabilities of digital equipment. A key element is a device known as an analog-to-digital converter (A / D converter), which is a critical front end for many systems. However, since the performance of the A / D converter is inferior to that of a digital processing device, it is an obstacle to complete digitization for many applications.
[0003]
An A / D converter that operates between 30 MHz and 3 GHz with a resolution exceeding about 10 bits is desired. These A / D converters can be used as components such as radar front ends, jamming receivers, image processing, HDTV, and others. Since the conventional semiconductor device has a known system limitation, it cannot satisfy the performance required above. For example, current silicon bipolar technology is expected to achieve 4 bit resolution at 1 GHz, and gallium arsenide heterojunction bipolar transistor (HBT) is expected to achieve 6 bit resolution at 1 GHz. This leaves room for Josephson Junction (JJ) technology to be most likely to deliver the performance required for modern digital systems. The fastest Josephson junction flash A / D converter operating at liquid He temperature achieved 6 bits at 1 GHz and 3 bits at 10 GHz. These low critical temperature (Tc) circuits require high quality Josephson junctions with high nonlinearities that cannot be reproduced using high Tc (HTC) superconductivity. Thus, many well known low Tc Josephson junction circuits and their concepts are considered infeasible in HTC superconductivity. It is therefore reasonable to conclude that this kind of well-known technology reaches a fundamental limit at the capability level, and pursuing new methods is justified and timely.
[0004]
Therefore, there is a need in the art for a new A / D conversion system and method based on HTC superconductivity that produces orders of higher capability levels than was thought possible by using conventional low Tc Josephson junction devices. Remains as before. In particular, there is a need for an A / D conversion system that has a bandwidth capability in excess of 10 GHz with a resolution of 10 bits, which cannot be achieved by known techniques.
DISCLOSURE OF THE INVENTION
[Means for Solving the Problems]
[0005]
The prior art discussed above and other problems and deficiencies are due to several methods and apparatus according to the system and method for converting an analog voltage signal to a digital representation, known as the A / D converter of the present invention. Overcoming or mitigated.
[0006]
The present invention teaches an N-bit A / D converter made with N superconducting, preferably HTC, transmission lines. The N lines are arranged in parallel and close to each other. On each line, 2 N ^{- 1} Josephson junction device is embedded in series. Therefore, the Josephson junction element forms a matrix on the configuration of N superconducting transmission lines, whereby the Josephson junction element gives an N-digit binary number in a direction crossing the transmission line. The N-digit binary numbers are arranged in integer order along the direction. A scanning electron beam is generated to strike the device. This beam is scanned across the transmission line at a high frequency, while it is deflected along the line direction by the applied voltage. The beam causes a voltage step on each of the N transmission lines to strike any one of the N Josephson junction elements. In this way, an N-bit step voltage pattern is generated on the transmission line by cross scanning of each beam. This pattern is a direct reading of the input voltage signal.
[0007]
The above discussed and other features and advantages of the present invention will be understood by those skilled in the art from the following detailed description and drawings.
BEST MODE FOR CARRYING OUT THE INVENTION
[0008]
The present specification is based on an HTC superconducting weak link element capable of producing higher performance level orders than would have been possible using conventional low Tc Josephson Junction (JJ) elements. A novel A / D converter system and method are disclosed. This system relies on two phenomena. First, the electron beam can be deflected within a frequency range of several GHz. Second, the Josephson junction element (JJ) is converted to a voltage state when it is hit by an appropriate electron beam. This ultra high performance A / D converter utilizes electron beam interaction with superconducting elements and circuitry. In particular, the systems and methods disclosed herein can deflect an electron beam with a bandwidth greater than 10 GHz, and can provide an A / D converter with 10-bit resolution and 10 GHz bandwidth performance. This has been impossible to achieve with conventional techniques. This hybrid system also benefits from the important low isolation nature of superconducting transmission lines and the ultrafast switching of HTC weak links. In one embodiment, a 12-bit A / D converter with an analog bandwidth from 500 MHz to 1 GHz is feasible. This is a high order according to other technologies. In another embodiment, the performance of the A / D converter can be improved to 10 GHz with 12 bits.
[0009]
It is well known that Josephson junction devices are switched from a zero voltage state to a finite voltage state when excited by an energetic electron beam. This beam produces quasiparticles that suppress the Josephson current. Figure 1 is a current-voltage characteristic of the Josephson device of the weak link type, which has a critical current J _o, which is a biased current at a current I _g. If the electron beam is applied, J _o is suppressed _(lower of I _g) I _'o, to switch the device from the zero voltage state to V _o. The device is reset to a zero voltage state when the electron beam excitation is removed. It is well known that the switching speed of weak link type Josephson junction devices is in the subpicosecond range. To achieve this, the energy E _e of the electron beam must at the same time be on the order of Josephson energy E _j = I _o M _o / 2B, where E _e is more than the superconducting condensation energy. Must be very small. When using a Josephson device, I _o is in the range of 0.1 to ImA, the electron beam current and voltage are a few μA and a few KV, respectively, and the beam excitation pulse period is 1-10 picoseconds. The condition of being in the range can be easily satisfied.
[0010]
FIG. 2 shows a transmission line 20 as a component of the multi-bit A / D converter system disclosed herein. The transmission line 20 is a non-dispersive HTC superconducting transmission line that continuously includes a plurality of Josephson junctions 22 (as shown by the cross section of FIG. 2). Transmission line 20 is generally _{Z o} has characteristic impedance effect of (several ohms) and are matched (matched) at both ends. Current supply biases the Josephson junction in I _g, and, as indicated above, when the electron beam that hits in any one of these junctions, the voltage pulse V _o is generated, the line output of the Sent to the end. This transmission line has a length L that defines a signal transmission delay time T from left to right, where T is V _p is the transmission line phase velocity and, in practical circumstances, 1 of the speed of light. T = L / _vp when equal to / 3. The transmission delay time generally limits the resolution bandwidth and bits of the A / D converter.
[0011]
Therefore, the A / D converter includes the N transmission lines 20 shown in FIG. The principle of operation is shown in FIG. 3, in which a 3-bit A / D converter 30 is shown. In this case, the three transmission lines 32a, 32b and 32c are located adjacent to each other and are separated by a suitable distance to minimize crosstalk. These transmission lines 32a, 32b and 32c are provided along the Y direction, and the electron beam is swept or scanned along the X direction. Also shown in FIG. 3 are 2 ³ or 8 rows indicated by Y ₀ through Y ₇ . In the XY plane, a matrix having eight rows and three columns (three transmission lines 32a, 32b and 32c) is formed. The bit pattern indicating the position of each row is indicated by the Josephson junction (X) number of each row. For example, the first row, Y _o does not have a Josephson junction element, and the bit pattern indicating the Y _o position is (0, 0, 0). On the other hand, Y ₇ has three Josephson junction elements and the bit pattern is (1, 1, 1). In order to achieve the A / D converter function, this utilizes the ability to scan the electron beam in the XY plane direction very quickly. Electron beam deflection with a bandwidth approaching 20 GHz is possible. In the X direction, the electron beam is continuously swept at the sampling frequency f _s (f _s > 10 GHz). Input analog signal is applied to the Y deflection system, the beam in the Y direction, depending on the value of the input analog signal, from the Y _o at a position between the Y _7, deflects. For example, if the input analog signal is zero, the electron beam is swept across the first row (Y _o ) in the X direction, and in this case there is no Josephson junction in this row, so there are three lines The output voltage of is a bit pattern (0.0.0). At the highest input voltage, the beam is deflected in the Y direction so that it can traverse the eighth row (Y ₇ ), and the three Josephson junctions switch (according to FIGS. 1 and 2). And the output is a bit pattern (1, 1, 1). Of course, if the value is between zero and the highest value, the beam will sweep across other rows. As the analog signal changes, the output bit pattern changes to reflect it at the sampling frequency f _s . It should be understood by those skilled in the art that a Josephson junction element is assigned to “1” and assigned to override “0” or vice versa. It is optional.
[0012]
The 3-bit A / D converter 30 obviously depends on the zero resistance and non-dispersive quality of the superconducting transmission line, the extremely high switching speed of the Josephson junction and the ability to deflect the electron beam at several GHz in the XY direction. ing.
[0013]
In FIG. 4, an N-bit general A / D converter 40 is shown. Here, of course, N transmission lines 42a, 42b, 42c. . . 42 _N-1 is required. The row repeats with period p and with the length of the Josephson junction element, and it is also the length of the void, ie the shortest part of the line without the Josephson junction element. The total length of each transmission line is L = p2 ^N. This relationship indicates that if L is kept constant, the number of bits increases as the value of p decreases, thereby allowing a wider analog bandwidth. The analog bandwidth is limited by the propagation delay T of the signal in the transmission line 42, which is related to the length of the transmission line. The bandwidth of the A / D converter 40 can be expressed as BW = 1 / 2T.
[0014]
The sampling frequency is the frequency at which the electron beam is swept in the X direction, which determines the maximum performance of the system. Maximum analog bandwidth BW of the system can not exceed 1 / 2f _s. As shown in FIG. 5, the performance of the A / D converter is generally partitioned by three lines or regions.
[0015]
The flat region is limited by the relationship of the electron beam deflection bandwidth in the Y-direction, f _s and BW = f _s / 2. Only if the sampling interval is longer than approximately 3T, analog bandwidth BW = f s / ₂ is independent of the bits representing the resolution. If P = 0.5 microns and the beam size is equal to 0.5 microns in diameter, f _s = 20 GHZ gives a maximum analog bandwidth of 10 GHz and a maximum bit number N = 13.
[0016]
Light limits the area, ie if N> 13, the bandwidth is related to the number of bits as shown in the following formula: BW = (c / 2np) x (1/2 ^N ) where , C is the speed of light, n reflects how slow the transmission line phase speed is compared to c, individually processed to be 3 and p is the pitch. From this equation, 1 GHz BW and N = 17 bits are obtained.
[0017]
In the above formula, since the transmission line length is not infinitely long, the maximum length limit shown in FIG. 5 is given. Based on experience-based intuition, practical constraints such as micro-device fabrication, electron beam scan distance, beam defocus, etc., the maximum transmission line length is about 10 cm, in this case the performance of the A / D converter Has a resolution of 18 bits with a bandwidth of 500 MHz.
[0018]
By setting the pitch to 0.5 microns or less and the electron beam deflection bandwidth to be larger than 20 GHz, the performance can be further improved as shown by the dashed curve in FIG. Both can be realized by advanced lithography and micro-element manufacturing techniques, along with precise design of the electron beam deflection system.
[0019]
From the above analysis, it is clear that the electron beam A / D converter of the present invention has a higher performance order than the most advanced Josephson junction circuit. The possibility of obtaining an analog bandwidth of 10 GHz with 13-bit resolution, or 1 GHz with 17 bits, is impossible to contemplate using other techniques. A key factor to achieving this type of extremely high performance level is the ability to produce electron beam deflection circuits with bandwidths in excess of 10 GHz. This is because S.A. M.M. Kokimski (IEEE Transitions on Electron Devices, Vol. 38. page 1524, June, 1991). Another important effect of this novel concept is that the Josephson junction can be of weak link type rather than a tunnel junction with sharp quasi-particle tunneling components. The weak link can be made immediately using HTC superconducting material, so that it can be cooled to 77 ° K in the miniature refrigerator shown in FIG.
[0020]
The main problem with achieving a deflection bandwidth of 20 GHz or above is related to linearity in the dynamic range above 2 ^N for N> 10. Fortunately, the disclosed A / D converter architecture can be addressed with a superconducting chip. Instead of rows that repeat periodically at pitch p, a group of rows has a variable space determined by non-linear measurements. This scheme can therefore minimize non-linearity.
[0021]
A preferred embodiment of an ultra high performance A / D converter system 70 is shown schematically in FIG. The A / D converter system 70 includes three large subsystems. The electron beam subsystem 76 is known, for example, with the ability to generate and transmit an electron beam with a voltage in the range of 1-5 KV, depending on the desired analog bandwidth, eg, 0.5 micron diameter, 0.1 μA. It has an electron beam generator. Depending on performance, the XY direction deflection circuit is designed to achieve a bandwidth in the range of 100 MHz to 200 GHz.
[0022]
Superconducting transmission line tip 76, is provided along with the appropriate insulation and resistor technology and regulated source, it is a linear transmission of achievable as described with respect to FIGS. 2-4, high T _c superconductors A transmission line and a weak link element are used. Chip 76 preferably includes a wide bandwidth amplifier for interfacing room temperature electronics. The chip 76 must be packaged in a vacuum seal device so that the top side is in a vacuum state, and the other surface is connected to a thermally cooled subsystem 78 and subjected to electron beam excitation.
[0023]
A cooling subsystem 78 is provided to compensate for the disappearance of the milliwatt fraction of the power supply from the superconducting circuit. Therefore, the cooling limit is not severe. For example, cooling can be accomplished simply using the miniature Stirling cycle refrigerator shown in FIG. 6, which is well known.
[0024]
Additional electronic components, not specifically shown in FIG. 7, may also be used for specific applications, such as linear wide bandwidth amplifiers, simultaneity generators and room temperature interface electronic components, memory buffers and processors. Can be included as needed.
[0025]
The modifications to the various aspects of the invention described above are merely exemplary. It will be appreciated that other modifications to the illustrated embodiment will immediately occur to those skilled in the art. All such modifications and changes are considered within the spirit and scope of the invention as defined in the claims.
[Brief description of the drawings]
[0026]
FIG. 1 shows current-voltage characteristics of a weak link Josephson junction element.
FIG. 2 shows a low dispersive HTC superconducting line excited by an electron beam, matching at both ends and including a series of weak links.
FIG. 3 shows a 3-bit electron beam excited superconducting A / D converter.
FIG. 4 shows a typical N-bit, beam-excited superconducting A / D converter.
FIG. 5 shows the expected capability of the electron beam A / D converter of the embodiment as an example.
FIG. 6 shows a miniature Stirling closed cycle refrigerator.
FIG. 7 shows a schematic diagram of an ultra-high performance analog-to-digital converter system.

Claims (6)

A system for obtaining information about the size of a voltage signal,
A superconducting transmission line having a starting point;
One or two or more Josephson junction elements, embedded in the superconducting transmission line, and arranged at a predetermined interval from the starting point; and
An electron beam that is applied to the superconducting transmission line, the electron beam being received so as to be displaced along the direction of the superconducting transmission line by an amount proportional to the magnitude of the voltage signal; And the electron beam generates a voltage step on the superconducting transmission line in a state where it hits any one of the one or more Josephson junction elements. The system of claim 1, further comprising:
N-1 additional superconducting transmission lines, wherein the N-1 additional superconducting transmission lines are arranged in close proximity and substantially parallel to each other, together with the superconducting transmission line Giving a configuration consisting of N substantially identical superconducting transmission lines, the configuration having two characteristic directions: a Y direction along the transmission line and an X direction across the transmission line; The additional transmission line;
A matrix of Josephson junction elements embedded on an N superconducting wire configuration, the matrix being formed from 2 ^N-1 Josephson junction elements on each one of the ^N superconducting lines. Here, the Josephson junction element includes a matrix in which N-digit binary numbers are arranged in numerical order along the X direction, and further, the N-digit binary numbers are arranged in numerical order along the Y direction;
It comprises voltage scanning for deflecting the electron beam in the x direction so that the electron beam periodically hits each of the N superconducting transmission lines. The system of claim 2, wherein the superconducting transmission line is formed of an HTC superconductor material. The system of claim 3, wherein
A cooling subsystem that provides an environment in which the HTC superconductor material conducts current without resistance;
An electron beam subsystem further comprising an aspirator system. A method of taking an N-bit digital sample of a time-varying voltage signal,
Providing N superconducting transmission lines, the N additional superconducting transmission lines being arranged close to each other and substantially parallel to each other in two characteristic directions: Providing a configuration having a Y direction along the transmission line and an X direction across the transmission line; and
The step of successively embedding 2 ^N-1 Josephson junction elements on each of the N superconducting wire configurations, wherein the Josephson junction device has a matrix on the configuration of the N superconducting transmission lines. The Josephson junction element is configured such that an N-digit binary number is generated along the X direction, and the N-digit binary numbers are arranged in an integer order along the Y direction. When,
Applying an electron beam onto the array of N superconducting transmission lines, wherein the electron beam is deflected in the X direction by a scanning voltage, and the electron beam is periodically applied to each of the N superconducting transmission lines. The electron beam is also received so as to be deflected in the Y direction in proportion to the size of the time-varying voltage signal, and the electron beam hits one of the Josephson junction elements. Generating a voltage step on any one of the superconducting transmission lines, whereby the voltage step on the N lines is a digital representation of the time-varying voltage signal;
Having a method. 6. The method of claim 5, further comprising selecting an HTC superconductor material for constructing the superconducting transmission line.

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